The purpose of the present proposal is to study the dynamics of gas exchange at the levels of the lung, blood, and tissue. The following studies are proposed: 1) To further analyze changes in VA/Q ratio distribution in response to environmental stress; 2) to assess the time-dependent changes in VA/Q ratio distribution and in pulmonary shunt in patients during the progression of adult respiratory distress syndrome; and 3) to develop a model of the systemic tissue capillary gas exchange. BIBLIOGRAPHIC REFERENCES: Hlastala, M. P. and R. D. Woodson. Saturation dependency of the Bohr effect: interactions among H ions, CO2 and DPG. J. Appl. Physiol. 38:1126-1131, 1975. Hlastala, M. P. and H. D. Van Liew. Absorption of in vivo inert gas bubbles. Respir. Physiol. 24:147-158, 1975.